Wire rod for 55kg grade gas shielded welding wire and preparation method thereof

Abstract

The application provides a 55kg-grade wire rod for gas shielded welding wire and a preparation method, and belongs to the field of wire rod production. The method comprises the following steps: obtaining a blank with a set chemical composition; performing wire laying of the blank at a set temperature to obtain a loose coil; and performing Stelmor cooling on the loose coil, then performing coiling and cooling to obtain a wire rod; wherein the Stelmor cooling comprises the following parameters: loose coil non-lap point into heat preservation cover temperature, loose coil non-lap point out of heat preservation cover temperature, loose coil lap point out of heat preservation cover temperature, loose coil non-lap point cooling rate and segmented control roller speed. The process idea of adopting a higher wire laying temperature and appropriately increasing the roller speed is adopted, the non-lap point completes the phase change from austenite to ferrite and bainite in the heat preservation cover, the lap point position completes the ferrite phase change when it comes out of the heat preservation cover, and the remaining austenite changes into bainite during the slow cooling after coiling, so that the same coil performance of the 55kg-grade wire rod for gas shielded welding wire is improved.

Description

Technical Field

[0001] This application relates to the field of wire rod production technology, and in particular to a 55kg grade gas shielded welding wire wire rod and its preparation method. Background Technology

[0002] The main production process of gas-shielded welding wire rod is as follows: molten iron → converter (electric furnace) smelting → LF refining → VD (RH) vacuum smelting → tundish → continuous casting → continuous casting billet → high-speed wire rod workshop → heating → rough rolling → intermediate rolling → finish rolling (RSM) → wire drawing → Stellmore delayed cooling line → coiling → inspection → packaging → warehousing. The main manufacturing process of gas-shielded welding wire is as follows: (annealing) → wire rod → mechanical peeling → pickling → rough drawing → (annealing) → fine drawing → rinsing and copper plating → polishing → winding and coiling → inspection → packaging → warehousing. It is necessary to... or The standard wire rods are coarsely drawn and finely drawn into finished welding wire specifications. The total reduction in surface area during drawing deformation reaches 92-98%. Therefore, the wire rod is required to have good drawing performance (plasticity). In order to ensure a smooth drawing process, high-strength welding wire needs to undergo annealing and softening treatment before or during drawing, depending on the strength of the wire rod or welding wire.

[0003] During the manufacturing process of 55kg-grade gas-shielded welding wire rods, the rods are coiled and laid out on the Stellmore cooling line. The thickness of the coil buildup differs between overlapping and non-overlapping points, resulting in different cooling rates and varying ferrite + bainite microstructure ratios and strengths. The metallographic structures corresponding to different strengths at overlapping and non-overlapping points differ, and the co-coil performance (the difference between the maximum and minimum tensile strength values ​​obtained from samples taken from different locations within the same coil) exceeds 100 MPa. Due to this poor co-coil performance, users must anneal the rods before use. Therefore, improving the co-coil performance of 55kg-grade gas-shielded welding wire rods to achieve anneal-free drawing is a pressing technical problem that needs to be solved. Summary of the Invention

[0004] This application provides a 55kg grade gas shielded welding wire rod and its preparation method to solve the following technical problem: how to improve the coil performance of the 55kg grade gas shielded welding wire rod.

[0005] In a first aspect, this application provides a method for preparing 55kg-grade gas-shielded welding wire rod, the method comprising:

[0006] Obtain a blank with a set chemical composition;

[0007] The blank is spun at a set temperature to obtain loose coils; and

[0008] The loose coil is subjected to Stellmore cooling, followed by coiling and cooling to obtain wire rod; wherein, the Stellmore cooling includes the following parameters: temperature of the loose coil entering the insulation cover at the non-overlapping point, temperature of the loose coil exiting the insulation cover at the non-overlapping point, temperature of the loose coil exiting the insulation cover at the overlapping point, cooling rate of the loose coil at the non-overlapping point, and speed of the segmented control roller conveyor.

[0009] Optionally, the set temperature for spinning is 950℃~980℃.

[0010] Optionally, the temperature at which the uncoiled non-overlapping point enters the insulation cover is ≥800℃, and the temperature at which the uncoiled non-overlapping point exits the insulation cover is ≤450℃.

[0011] Optionally, the temperature of the insulation cover at the loose roll overlap point is 580℃~680℃.

[0012] Optionally, the cooling rate of the non-overlapping points of the loose roll is ≤0.6℃ / s.

[0013] Optionally, the segmented control of the roller conveyor speed includes the following: the first to thirteenth roller conveyor speeds of the Stellmore Cooling section are 0.15 m / s, 0.16 m / s, 0.16 m / s, 0.17 m / s, 0.17 m / s, 0.18 m / s, 0.18 m / s, 0.19 m / s, 0.19 m / s, 0.20 m / s, 0.27 m / s, 0.38 m / s, and 0.53 m / s, respectively.

[0014] Optionally, the winding assembly includes the following parameters: winding temperature at the overlap point of the loose winding ≥ 550℃, and the cooling rate ≤ 0.4℃ / s.

[0015] Optionally, the specified chemical composition includes: C, Si, Mn, P, S, Cr, Mo, and Fe; by mass fraction, the content of C is 0.06%–0.10%, the content of Si is 0.50%–0.70%, the content of Mn is 1.35%–1.55%, the content of P is ≤0.015%, the content of S is ≤0.012%, the content of Cr is 1.25%–1.50%, and the content of Mo is 0.40%–0.60%.

[0016] Secondly, this application provides a wire rod prepared by the method described in any one of the embodiments of the first aspect, wherein the metallographic structure of the wire rod comprises ferrite and bainite, wherein the ferrite content is ≥60% by volume fraction, and the microhardness of the bainite is ≤500HV.

[0017] Optionally, the wire rod meets the following performance requirements: tensile strength of 650 MPa to 720 MPa, same-coil performance ≤ 50 MPa, and can be used without annealing and drawing.

[0018] The technical solutions provided in this application have the following advantages compared with the prior art:

[0019] This application provides a method for preparing 55kg-grade gas-shielded welding wire rod, comprising: obtaining a billet with a set chemical composition; spinning the billet at a set temperature to obtain loose coils; and subjecting the loose coils to Stellmore cooling, followed by coiling and cooling to obtain wire rods. The Stellmore cooling includes the following parameters: temperature at which the non-overlapping point of the loose coil enters the insulation hood, temperature at which the non-overlapping point of the loose coil exits the insulation hood, temperature at which the overlapping point of the loose coil exits the insulation hood, cooling rate at the non-overlapping point of the loose coil, and segmented control of the roller speed. By employing a higher spinning temperature and appropriately increasing the roller speed, the non-overlapping points undergo austenite to ferrite and bainite phase transformation within the insulation hood; simultaneously, the overlapping points undergo ferrite phase transformation upon exiting the insulation hood, and the remaining austenite undergoes bainite phase transformation during slow cooling after coiling. This helps reduce the strength difference between the overlapping and non-overlapping points of the wire rod, thereby improving the coil performance of the 55kg-grade gas-shielded welding wire rod. Attached Figure Description

[0020] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0021] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0022] Figure 1 CCT curve of 55kg-grade gas-shielded welding wire rod provided in the embodiments of this application;

[0023] Figure 2 A schematic flowchart illustrating a method for preparing a 55kg-grade gas-shielded welding wire rod according to an embodiment of this application;

[0024] Figure 3 Metallographic diagrams of the non-lap joint (a) and lap joint (b) of the wire rod provided in Embodiment 1 of this application;

[0025] Figure 4 Metallographic diagrams of the non-lap joint (a) and lap joint (b) of the wire rod provided in Comparative Example 1 of this application;

[0026] Figure 5 Metallographic diagrams of the non-lap joint (a) and lap joint (b) of the wire rod provided in Comparative Example 2 of this application. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0028] Various embodiments of this application may exist in the form of a range; it should be understood that the description in the form of a range is merely for convenience and brevity and should not be construed as a hard limitation on the scope of this application; therefore, it should be considered that the range description has specifically disclosed all possible sub-ranges and single numerical values ​​within that range. For example, it should be considered that the range description from 1 to 6 has specifically disclosed sub-ranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., and single numbers within the range, such as 1, 2, 3, 4, 5, and 6, regardless of the range. Furthermore, whenever a numerical range is referred to herein, it means including any referenced number (fraction or integer) within the referred range.

[0029] Furthermore, in the description of this application, the terms "comprising," "including," etc., mean "including but not limited to." In this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. In this document, "and / or" describes the relationship between related objects, indicating that three relationships can exist; for example, A and / or B can represent: A alone, A and B simultaneously, or B alone. A and B can be singular or plural. In this document, "at least one" means one or more, and "more than" means two or more. "At least one," "at least one of the following," or similar expressions refer to any combination of these items, including any combination of single or plural items. For example, "at least one of a, b, or c" or "at least one of a, b, and c" can both mean: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, and c can be a single or multiple.

[0030] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this application can be purchased from the market or prepared by existing methods.

[0031] The inventive concept of this application is as follows:

[0032] The 55kg grade gas-shielded welding wire of this invention is a high-strength, heat-resistant welding wire steel with high content of alloying elements such as Cr, Mn, and Mo, resulting in high hardenability and a high bainite content. After being coiled, the wire rod from the high-speed wire rod mill is stacked in a coil on the moving roller conveyor. The stacking density and cooling rate of the wire rod on the roller conveyor can be adjusted by changing the roller conveyor speed. The cooling rate can also be adjusted by adding an insulation cover to the cooling roller conveyor. After being coiled and coiled, the wire rod is scattered in a coil on the slow-cooling roller conveyor, forming overlapping points on both sides of the roller conveyor and non-overlapping points in the middle. The overlapping points have higher temperatures and slower cooling rates, while the non-overlapping points have lower temperatures and faster cooling rates. Different positions on the same coil result in different cooling rates, metallographic structures, and strength properties. For welding wire steel, the traditional production process involves low coiling temperature, low roller speed, and full insulation to reduce the cooling rate of the wire rod and obtain as much ferrite with good plasticity as possible and as little bainite as possible. However, for the high-strength heat-resistant welding wire steel of this invention, in traditional processes, a lower roller speed is used to obtain as much ferrite content as possible. However, the temperature at the overlap point when exiting the insulation cover is relatively high, falling within the bainitic transformation temperature range (580℃~450℃). Bainitic transformation occurs under air cooling conditions (cooling rate greater than 1℃ / s) before coiling, resulting in bainitic strengthening. Although the ferrite content at both the overlap and non-overlap points is >60%, the difference in bainitic hardness leads to poor tensile strength and co-coil performance in the wire rod. The metallographic structures corresponding to different strengths at the overlap and non-overlap points are different, with co-coil performance exceeding 100MPa. Due to the poor co-coil performance of the wire rod, users must anneal it before use.

[0033] The CCT curves obtained from thermal simulation tests of the steel grades according to the present invention are shown in the appendix. Figure 1 It is known that the ferrite + bainite phase transformation temperature range of the 55kg-grade gas-shielded welding wire rod of the Cr, Mn, and Mo series of this invention is relatively wide, with the ferrite phase transformation temperature range being 800℃~680℃ and the bainite phase transformation temperature range being 580℃~450℃. To obtain a metallographic structure with good plasticity, it is desirable that both the ferrite and bainite structures undergo phase transformation within the insulation hood (with an average cooling rate of less than 0.6℃ / s). However, under the limiting capacity conditions of existing equipment, due to the temperature difference between the overlapping and non-overlapping points, it is difficult to achieve ferrite and bainite phase transformation at both overlapping and non-overlapping points within the insulation hood. If the goal is for the ferrite and bainite phase transformations at the lap joints to occur entirely within the insulation cover, then the temperature at which the non-lap joints enter the insulation cover might be too low, resulting in an excessive amount of bainite or even a completely bainite structure. If the goal is for the ferrite and bainite phase transformations at the non-lap joints to occur entirely within the insulation cover, then the temperature at the lap joints exiting the insulation cover would be too high, potentially leading to the bainite phase transformation at the lap joints being completed under air-cooling conditions (cooling rate greater than 1℃ / s) after exiting the insulation cover and before coiling.

[0034] Based on the aforementioned technical problems, the production method provided in this invention differs from the traditional process approach of using low wire-drawing temperatures to reduce hardenability and extremely slow roller speeds. Instead, it employs a higher wire-drawing temperature and appropriately increased roller speed. The non-lap joints are controlled to complete the austenite-to-ferrite-bainite phase transformation within the insulation hood (temperature range 800–450°C); simultaneously, the temperature at the lap joint exiting the insulation hood is controlled to be below 680°C (completing the ferrite phase transformation), and the coiling temperature at the lap joint is controlled to be above 550°C, allowing the remaining austenite to complete the bainite phase transformation under slow cooling after coiling. This application solves the problem of the wide phase transformation temperature range and large temperature difference between lap and non-lap joints in 55kg grade heat-resistant gas-shielded welding wire steel, which existing Stellmore cooling processes cannot achieve the ferrite-bainite phase transformation of the entire coil within the insulation hood. This invention helps to reduce the strength difference between the lap joints and non-lap joints of the wire rod, and the same coil performance is ≤50MPa, which can meet the requirements of users to use it without annealing during the drawing process of gas shielded welding wire.

[0035] Please see the appendix Figure 2 This application provides a method for preparing 55kg-grade gas-shielded welding wire rod, the method comprising:

[0036] S1. Obtain a blank with a set chemical composition;

[0037] In some embodiments, the specified chemical composition includes: C, Si, Mn, P, S, Cr, Mo, and Fe; by mass fraction, the content of C is 0.06% to 0.10%, the content of Si is 0.50% to 0.70%, the content of Mn is 1.35% to 1.55%, the content of P is ≤0.015%, the content of S is ≤0.012%, the content of Cr is 1.25% to 1.50%, and the content of Mo is 0.40% to 0.60%.

[0038] The chemical composition of the billet needs to be precisely controlled to ensure the performance and quality of the final product. Specific components include: Carbon (C): 0.06%–0.10%. Carbon is the main strengthening element in steel, significantly affecting its hardenability and strength. Silicon (Si): 0.50%–0.70%. As a deoxidizing and strengthening element, silicon improves the strength and hardness of the weld. Manganese (Mn): 1.35%–1.55%. Manganese significantly improves the hardenability of steel and promotes the formation of bainite. Phosphorus (P): ≤0.015%. Phosphorus is a harmful element in steel and its content must be strictly controlled. Sulfur (S): ≤0.012%. Sulfur is also a harmful element, adversely affecting the weldability of steel. Chromium (Cr): 1.25%–1.50%. Chromium improves the corrosion resistance and hardness of steel while promoting the formation of bainite. Molybdenum (Mo): 0.40%–0.60%. Molybdenum enhances the hardenability and hot strength of steel, improving the strength and toughness of welds. In this invention, the high content of alloying elements such as Cr, Mn, and Mo results in high hardenability of the steel and a high content of bainite in the obtained structure. For example, the content of C can be 0.06%, 0.07%, 0.08%, 0.09%, 0.10%, etc.; the content of Si can be 0.50%, 0.55%, 0.60%, 0.65%, 0.70%, etc.; the content of Mn can be 1.35%, 1.40%, 1.45%, 1.50%, 1.55%, etc.; and the content of P can be 0.005%, 0.007%, 0.009%, etc. The content of sulfur (S) can be 0.010%, 0.012%, 0.015%, etc.; the content of sulfur (S) can be 0.005%, 0.007%, 0.009%, 0.010%, 0.012%, etc.; the content of chromium (Cr) can be 1.25%, 1.30%, 1.35%, 1.40%, 1.45%, 1.50%, etc.; and the content of molybdenum (Mo) can be 0.40%, 0.45%, 0.50%, 0.55%, 0.60%, etc.

[0039] S2. The blank is spun at a set temperature to obtain loose coils; and

[0040] In some embodiments, the set temperature for spinning is 950°C to 980°C.

[0041] The advantages of limiting the wire drawing temperature to 950℃~980℃ are: A higher wire drawing temperature results in a relatively higher entry temperature at the non-overlapping joints, ensuring that the ferrite phase transformation at these joints completes entirely within the insulation shroud, resulting in coarse ferrite grains and reducing the strength of the wire rod. Simultaneously, it helps to increase the exit temperature at the overlapping joints, preventing bainitic phase transformation during exit and instead postponing the transformation process until after coiling. The wire drawing temperature can be 950℃, 955℃, 960℃, 970℃, 975℃, 980℃, etc.

[0042] S3. The loose coil is subjected to Stellmore cooling, followed by coiling and cooling to obtain wire rod; wherein, the Stellmore cooling includes the following parameters: temperature of the loose coil entering the insulation cover at the non-overlapping point, temperature of the loose coil exiting the insulation cover at the non-overlapping point, temperature of the loose coil exiting the insulation cover at the overlapping point, cooling rate of the loose coil at the non-overlapping point, and speed of the segmented control roller conveyor.

[0043] The present invention installs heat insulation covers on the Stellmore cooling line. Cooling is controlled by controlling the number of heat insulation covers on the Stellmore cooling line. Depending on the temperature inside the cover (seasonal factors), the first one, two or three heat insulation covers are opened, and the remaining heat insulation covers are closed.

[0044] In this embodiment of the application, the temperature at the non-overlapping point entering the cover also represents the "insulation start temperature at the non-overlapping point", the temperature at the overlapping point exiting the cover also represents the "insulation end temperature at the overlapping point", and the cooling rate inside the non-overlapping point cover also represents the "cooling rate at the non-overlapping point".

[0045] In some embodiments, the temperature at which the uncoiled non-overlapping point enters the insulation cover is ≥800℃, and the temperature at which the uncoiled non-overlapping point exits the insulation cover is ≤450℃.

[0046] The positive effects of limiting the temperature of the non-overlapping point of the coiled coil entering the insulation cover to ≥800℃ and the temperature of the non-overlapping point exiting the insulation cover to ≤450℃ are as follows: According to the CCT curve, within this temperature range, the non-overlapping point can complete the ferrite and bainite phase transformation within the insulation cover. The entry temperature of the non-overlapping point of the coiled coil into the insulation cover can be 800℃, 810℃, 820℃, 830℃, 840℃, 850℃, etc., and the exit temperature of the non-overlapping point of the coiled coil into the insulation cover can be 450℃, 440℃, 430℃, 420℃, 410℃, 400℃, etc.

[0047] In some embodiments, the temperature at the overlap point of the loose roll of insulation cover is 580°C to 680°C.

[0048] The positive effects of limiting the insulation end temperature of the lap joint to 580-680℃ are as follows: the ferritic phase transformation is completed before the lap joint exits the cover, and the bainitic phase transformation has not yet started before the coil is reassembled after exiting the cover. Otherwise, the bainitic phase transformation would occur immediately during air cooling after exiting the cover, resulting in increased bainite hardness, excessively high strength, and poor performance within the same coil. The temperature at which the lap joint exits the insulation cover can be 580℃, 590℃, 600℃, 610℃, 620℃, 630℃, 640℃, 650℃, 660℃, 670℃, 680℃, etc.

[0049] In some embodiments, the cooling rate of the uncoiled non-overlapping point is ≤0.6℃ / s.

[0050] The positive effects of limiting the cooling rate at non-overlapping points to ≤0.6℃ / s include: lower cooling rates result in more ferrite and less bainite, with the bainite structure also having lower hardness. The cooling rate can be adjusted by adding an insulation cover or adjusting the roller speed on the cooling line. Specifically, the cooling rate at the non-overlapping points can be 0.6℃ / s, 0.55℃ / s, 0.5℃ / s, 0.45℃ / s, 0.40℃ / s, 0.35℃ / s, 0.30℃ / s, etc.

[0051] In some embodiments, the segmented control of the roller conveyor speed includes the following: the first to thirteenth roller conveyor speeds at the Stellmore Cooling section are 0.15 m / s, 0.16 m / s, 0.16 m / s, 0.17 m / s, 0.17 m / s, 0.18 m / s, 0.18 m / s, 0.19 m / s, 0.19 m / s, 0.20 m / s, 0.27 m / s, 0.38 m / s, and 0.53 m / s, respectively.

[0052] The positive effects of segmented control of roller conveyor speed and the technical effects of the above-mentioned roller conveyor parameter settings: Through extensive experiments adjusting various process parameters, this application precisely achieves the cooling of the wire rod by combining the spinning temperature and the start and end temperatures of the insulation hood. Compared with the traditional process, the spinning temperature and the temperature entering the hood are increased. To prevent the temperature exiting the hood from being too high, this application proposes a technical solution to appropriately increase the speed of the roller conveyor inside the insulation hood to achieve an exit temperature of less than 450°C at the non-overlapping points.

[0053] In some embodiments, the winding assembly includes the following parameters: winding temperature at the unwinding overlap point ≥ 550°C, and cooling rate ≤ 0.4°C / s.

[0054] The positive effect of limiting the lap joint winding temperature to ≥550℃ is that bainitic phase transformation occurs at the lap joint after winding. If the temperature is too low, the bainitic phase transformation will occur during the air cooling process before winding. The lap joint winding temperature can be 550℃, 555℃, 560℃, 565℃, 570℃, 575℃, 580℃, etc.

[0055] The positive effect of limiting the cooling rate after coiling of wire rod to ≤0.4℃ / s is that a low cooling rate after coiling is beneficial for obtaining a bainitic microstructure with low hardness. The cooling rate after coiling ≤0.4℃ / s can be 0.4℃ / s, 0.35℃ / s, 0.3℃ / s, 0.25℃ / s, 0.2℃ / s, 0.15℃ / s, etc.

[0056] Based on a general inventive concept, this application provides a wire rod prepared by the method described in any of the above embodiments, wherein the metallographic structure of the wire rod comprises ferrite and bainite, wherein the ferrite content is ≥60% by volume fraction, and the microhardness of the bainite is ≤500HV.

[0057] This invention controls the austenite-to-ferrite-bainite phase transformation at the non-overlapping joints within the insulation cover (temperature range 800℃~450℃); simultaneously, it controls the temperature at the overlapping joints exiting the insulation cover to be below 680℃ (completing the ferrite phase transformation), and the coiling temperature at the overlapping joints to be above 550℃, allowing the remaining austenite to undergo the austenite-to-bainite phase transformation under slow cooling after coiling. For example, the ferrite content can be 60%, 62%, 65%, 67%, 70%, 72%, 75%, etc., and the microhardness of the bainite can be 440HV, 450HV, 460HV, 470HV, 480HV, 490HV, 500HV, etc.

[0058] In some embodiments, the wire rod meets the following properties: tensile strength of 650 MPa to 720 MPa, same-coil performance ≤ 50 MPa, and can be used without annealing and drawing.

[0059] This application helps to reduce the strength difference between lap joints and non-lap joints of the wire rod, with a coil strength of ≤50MPa, which can meet the requirements of users for annealing during the drawing process of gas-shielded welding wire. For example, the tensile strength of the wire rod can be 650MPa, 660MPa, 670MPa, 680MPa, 690MPa, 700MPa, 710MPa, 720MPa, etc., and the coil strength can be 40MPa, 42MPa, 44MPa, 46MPa, 48MPa, 50MPa, etc.

[0060] This wire rod is made based on the above-described wire rod preparation method. The specific steps of the preparation method can be referred to in the above embodiments. Since this wire rod adopts some or all of the technical solutions of the above embodiments, it has at least all the beneficial effects brought about by the technical solutions of the above embodiments, which will not be elaborated here.

[0061] The present application is further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the application. Experimental methods in the following embodiments that do not specify specific conditions are generally determined according to industry standards. If there is no corresponding industry standard, then common international standards, conventional conditions, or conditions recommended by the manufacturer are followed.

[0062] Example 1

[0063] This embodiment provides a 55kg grade gas shielded welding wire rod, which contains the following chemical elements by mass percentage: C: 0.06%, Si: 0.50%, Mn: 1.35%, P: 0.013%, S: 0.011%, Cr: 1.25%, Mo: 0.40%, with the balance being Fe.

[0064] This embodiment also provides a method for preparing 55kg grade gas-shielded welding wire rod, including: high-speed wire rod mill heating furnace → rough rolling → flying shear head → intermediate rolling → pre-finish rolling → high-speed finish rolling → water cooling → clamping and wire feeding → temperature-controlled coiling and cooling → coiling → wire rod inspection. Specifically, it includes the following steps:

[0065] The billet is spun into loose coils; the spun temperature is 950℃.

[0066] The loose coils are subjected to Stellmore cooling, followed by coiling and cooling to obtain wire rod. The Stellmore cooling process is as follows: After spinning, on the Stellmore cooling line, the first two insulation covers are opened, and the remaining insulation covers are closed, and all fans are turned off. The temperature at the non-overlapping point entering the cover is controlled at 800℃, and the temperature at the exit cover is 430℃. At this time, the temperature at the overlapping point exiting the cover is 580℃, and the cooling rate at the non-overlapping point is 0.5℃ / s. The roller speeds of the first to thirteenth sections of the Stellmore cooling line are 0.15m / s, 0.16m / s, 0.16m / s, 0.17m / s, 0.17m / s, 0.18m / s, 0.18m / s, 0.19m / s, 0.19m / s, 0.20m / s, 0.27m / s, 0.38m / s, and 0.53m / s, respectively. The coiling temperature at the overlap point is 550℃, and the cooling rate of the coil after coiling is 0.4℃ / s. The metallographic structure of the coil is as follows: Figure 3 As shown.

[0067] Example 2

[0068] This embodiment provides a 55kg grade gas shielded welding wire rod, which contains the following chemical elements by mass percentage: C: 0.08%, Si: 0.60%, Mn: 1.45%, P: 0.012%, S: 0.010%, Cr: 1.35%, Mo: 0.50%, with the balance being Fe.

[0069] This embodiment also provides a method for preparing 55kg grade gas-shielded welding wire rod, including: high-speed wire rod mill heating furnace → rough rolling → flying shear head → intermediate rolling → pre-finish rolling → high-speed finish rolling → water cooling → clamping and wire feeding → temperature-controlled coiling and cooling → coiling → wire rod inspection. Specifically, it includes the following steps:

[0070] The billet is spun into loose coils; the spun temperature is 970℃.

[0071] The loose coils are subjected to Stellmore cooling, followed by coiling and cooling to obtain wire rod. The Stellmore cooling process is as follows: After spinning, on the Stellmore cooling line, the first two insulation covers are opened, and the remaining insulation covers are closed, and all fans are turned off. The temperature at the non-overlapping point entering the cover is controlled at 810℃, and the temperature at the exit cover is 440℃. At this time, the temperature at the overlapping point exiting the cover is 620℃, and the cooling rate at the non-overlapping point is 0.45℃ / s. The roller speeds of the first to thirteenth sections of the Stellmore cooling line are 0.15m / s, 0.16m / s, 0.16m / s, 0.17m / s, 0.17m / s, 0.18m / s, 0.18m / s, 0.19m / s, 0.19m / s, 0.20m / s, 0.27m / s, 0.38m / s, and 0.53m / s, respectively. The temperature at the overlap point of the coil is 560℃, and the cooling rate of the coil after coiling is 0.35℃ / s.

[0072] Example 3

[0073] This embodiment provides a 55kg grade gas shielded welding wire rod, which contains the following chemical elements by mass percentage: C: 0.10%, Si: 0.70%, Mn: 1.55%, P: 0.015%, S: 0.012%, Cr: 1.50%, Mo: 0.60%, with the balance being Fe.

[0074] This embodiment also provides a method for preparing 55kg grade gas-shielded welding wire rod, including: high-speed wire rod mill heating furnace → rough rolling → flying shear head → intermediate rolling → pre-finish rolling → high-speed finish rolling → water cooling → clamping and wire feeding → temperature-controlled coiling and cooling → coiling → wire rod inspection. Specifically, it includes the following steps:

[0075] The billet is spun into loose coils; the spun temperature is 980℃.

[0076] The loose coils are subjected to Stellmore cooling, followed by coiling and cooling to obtain wire rod. The Stellmore cooling process is as follows: After spinning, on the Stellmore cooling line, the first two insulation covers are opened, and the remaining insulation covers are closed, and all fans are turned off. The temperature at the non-overlapping point entering the cover is controlled at 820℃, and the temperature at the exit cover is 450℃. At this time, the temperature at the overlapping point exiting the cover is 680℃, and the cooling rate at the non-overlapping point is 0.4℃ / s. The roller speeds of the first to thirteenth sections of the Stellmore cooling line are 0.15m / s, 0.16m / s, 0.16m / s, 0.17m / s, 0.17m / s, 0.18m / s, 0.18m / s, 0.19m / s, 0.19m / s, 0.20m / s, 0.27m / s, 0.38m / s, and 0.53m / s, respectively. The temperature at the overlap point of the coil is 580℃, and the cooling rate of the coil after coiling is 0.35℃ / s.

[0077] The metallographic structure, tensile strength, and coil properties of the wire rods obtained in Examples 1-3 are shown in Table 1.

[0078] Table 1. Metallographic structure, tensile strength, and coil properties of the wire rods obtained in Examples 1-3.

[0079]

[0080] Comparative Example

[0081] This comparative example provides a wire rod for gas shielded welding, and the chemical elements and contents of the wire rod are the same as those in Example 1.

[0082] This comparative example also provides a wire rod for gas-shielded welding wire, including the following steps:

[0083] After final rolling, the wire is spun out, with the spun-out temperature controlled at 820℃~840℃. The cooling line roller speed is set to the lowest possible speed (0.1m / s for the first section), and all insulation covers are closed. The temperature at the overlap point of the wire entering the cover is 780℃~720℃, and the temperature at the non-overlap point is 720℃~660℃. The temperature at the overlap point exiting the cover is 580℃~500℃, and the temperature at the non-overlap point exiting the cover is 480℃~400℃. After exiting the cover, the wire is air-cooled on the roller conveyor and then coiled. The specific process parameters for the preparation method of the comparative wire are shown in Table 2, and the metallographic structure, tensile strength, and coil properties of the wire prepared in the comparative example are shown in Table 3.

[0084] Table 2 shows the specific process parameters for the preparation methods of wire rod in the comparative examples.

[0085]

[0086] Table 3 shows the metallographic structure, tensile strength, and coil properties of the wire rods prepared in the comparative examples.

[0087]

[0088] From Tables 2 and 3 and Figure 4 , 5 It is evident that using traditional processes makes it difficult to balance the performance of both overlapping and non-overlapping joints.

[0089] In Comparative Example 1, when the lap joint temperature of the wire rod entering the shroud is 720°C and the exit temperature is 500°C, a relatively high ferrite content of 60% is obtained. At 500°C, the wire rod exiting the shroud is close to the bainitic transformation temperature range, and bainitic transformation occurs under air cooling. The microhardness of the bainite is 530 HV, and the wire rod strength is 710 MPa. Meanwhile, at the non-lap joint shroud temperatures of 660°C and 400°C, respectively, the bainitic transformation is largely completed within the shroud during exiting the shroud, resulting in a lower bainitic microhardness of 328 HV and a wire rod strength of 820 MPa. The same-coil strength of the wire rod is 110 MPa. In Comparative Example 2, when the lap joint temperature of the wire rod entering the shroud was 780°C and the exit temperature was 560°C, a relatively high ferrite content of 65% was obtained. However, at 560°C, the exit temperature was close to the bainitic transformation temperature range, and bainitic transformation occurred under air cooling conditions before coiling. The microhardness of the bainite was 558 HV, and the wire rod strength was 750 MPa. Meanwhile, the lap joint temperature and exit temperature were 720°C and 500°C, respectively. During exiting the shroud, the bainitic structure basically completed the phase transformation inside the shroud, resulting in a lower bainitic microhardness of 488 HV and a wire rod strength of 650 MPa. The same-coil performance of the wire rod was 100 MPa.

[0090] Using traditional processes, due to the temperature difference between the overlapping and non-overlapping points, it is difficult to ensure that the ferrite-bainite phase transformation occurs at both the overlapping and non-overlapping points within the insulation enclosure. If the goal is for the ferrite-bainite phase transformation at the overlapping points to occur entirely within the insulation enclosure, the temperature at which the non-overlapping points enter the enclosure might be too low, resulting in an excessive amount of bainite or even a completely bainite microstructure, as shown in the attached diagram. Figure 4 As shown in (a); if the goal is for the ferrite-bainite phase transformation at non-overlapping joints to occur entirely within the insulation shroud, then the temperature at the overlapping joints exiting the insulation shroud will be too high. Consequently, the bainite phase transformation at the overlapping joints may be completed under air-cooling conditions (cooling rate greater than 1℃ / s) after exiting the insulation shroud but before coiling, as shown in the attached diagram. Figure 5 As shown in (b).

[0091] Furthermore, one or more technical solutions in the embodiments of the present invention have at least the following technical effects or advantages:

[0092] In this embodiment of the invention, the tensile strength of the wire rod for gas shielded welding is 650 MPa to 720 MPa, and the same coil performance is ≤50 MPa.

[0093] In this embodiment of the invention, it is beneficial to reduce the strength difference between the lap joints and non-lap joints of the wire rod, and the same coil performance is ≤50MPa, which can meet the requirements of users to use it without annealing during the drawing process of gas shielded welding wire.

[0094] In this embodiment of the invention, unlike the traditional process approach of using low wire drawing temperature to reduce hardenability and extremely slow roll speed, a higher wire drawing temperature and appropriately increased roll speed are adopted. The non-overlapping points are controlled to complete the austenite-to-ferrite-bainite phase transformation within the insulation cover (temperature range of 800℃~450℃); simultaneously, the temperature at the overlapping points when exiting the insulation cover is controlled to be below 680℃ (completing the ferrite phase transformation), and the temperature at the overlapping points during coiling is above 550℃. The remaining austenite undergoes austenite-to-bainite phase transformation during slow cooling after coiling.

[0095] In this embodiment of the invention, the problem of the wide phase transformation temperature range and large temperature difference between the lap joint and non-lap joint of the steel used for 55kg-grade heat-resistant gas-shielded welding wire is solved, and the existing Stellmore cooling process cannot achieve the ferrite-bainite phase transformation of the entire coil within the heat insulation cover.

[0096] The above description is merely a specific embodiment of this application, enabling those skilled in the art to understand or implement this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A method for preparing 55kg grade gas-shielded welding wire rod, characterized in that, The method includes: Obtain a blank with a set chemical composition; The blank is spun at a set temperature to obtain loose coils; and The loose coil is subjected to Stellmore cooling, followed by coiling and cooling to obtain wire rod; wherein, the Stellmore cooling includes the following parameters: temperature of the loose coil entering the insulation cover at the non-overlapping point, temperature of the loose coil exiting the insulation cover at the non-overlapping point, temperature of the loose coil exiting the insulation cover at the overlapping point, cooling rate of the loose coil at the non-overlapping point, and speed of the segmented control roller conveyor. The set temperature for spinning silk is 950℃~980℃; The temperature at which the uncoiled non-overlapping point enters the insulation cover is ≥800℃, and the temperature at which the uncoiled non-overlapping point exits the insulation cover is ≤450℃. The temperature at the overlap point of the loose rolls outside the insulation cover is 580℃~680℃; The cooling rate of the non-overlapping points of the loose roll is ≤0.6℃ / s; The winding assembly includes the following parameters: winding temperature at the overlap point of the loose winding ≥ 550℃, and cooling rate ≤ 0.4℃ / s; The specified chemical composition includes: C, Si, Mn, P, S, Cr, Mo, and Fe; by mass fraction, the content of C is 0.06%~0.10%, the content of Si is 0.50%~0.70%, the content of Mn is 1.35%~1.55%, the content of P is ≤0.015%, the content of S is ≤0.012%, the content of Cr is 1.25%~1.50%, and the content of Mo is 0.40%~0.60%.

2. The method according to claim 1, characterized in that, The segmented control roller speeds include the following: the first to thirteenth roller speeds of the Stellmore Cooling section are 0.15 m / s, 0.16 m / s, 0.16 m / s, 0.17 m / s, 0.17 m / s, 0.18 m / s, 0.18 m / s, 0.19 m / s, 0.19 m / s, 0.20 m / s, 0.27 m / s, 0.38 m / s, and 0.53 m / s, respectively.

3. The method according to claim 1, characterized in that, The metallographic structure of the wire rod includes ferrite and bainite. The ferrite content is ≥60% by volume fraction, and the microhardness of the bainite is ≤500HV.

4. The method according to claim 1, characterized in that, The wire rod meets the following performance requirements: tensile strength of 650MPa~720MPa, same coil strength ≤50MPa, and can be used without annealing and drawing.

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